The code here is inspired by Brandon Simmons' zippo package, but uses
a slightly different approach to represent the Zipper that makes the whole thing
look like his breadcrumb trail, and can move side-to-side through traversals.

Restore ourselves to a location near our previously recorded position.

When moving left to right through a Traversal, if this will clamp at each level to the range 0 <= k < teeth,
so the only failures will occur when one of the sequence of downward traversals find no targets.